[imp] Login Problem after update to 5.2.2

[Kein Name]

Hello List,

I was running Horde Webmail 5.2.1 since the release without any trouble.
After updating Horde Webmail to 5.2.2 I have a strange problem every
other day (roughly one in 7 days).
I go to the login page and can see the login boxes, I enter
username/password and the log files show a login success for horde and
imp, so does the imap server.
BUT then I am not redirected to my mail box URL like this
https://webmail.example.net/imp/dynamic.php?page=mailbox#mbox:SU5CT1g
instead the login screen stays, with no error message on it and the URL
changes to something like
https://webmail.example.net/login.php?url=https%3A%2F%2Fwebmail.example.net%2Fimp%2Fdynamic.php%3Fpage%3Dmailbox&horde_logout_token=0JgcLt-y2mhIAbF5FgqIEQ3
and thats about it. I am not seeing my mailbox, I cannot re-try logging
in, as I always see the login boxes.

Does someone have an idea?

Thanks!

Bye
Stefan König